Electron-discharge device



May 13, 1930. L. K. MARSHALL 1,758,710

ELECTRON DISCHARGE DEVICE Filed Jan. 51, 1929 Patented -May 1-3, 1930UNITED STATES PATENT; OFFICE LAURENCE K. MARSHALL, OF CAMBRIDGE,MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO OLD COLONY TRUSTCOMPANY, A CORPORATION OF MASSACHU- SETTS ELECTRON-DISCHARGE DEVICE vApplication filed. January 31, 1929. Serial No. 336,463.

This invention relates to electron discharge devices and particularly tocathodes therefor. In such devices, the function of the cathode is toemit electrons and the greater 5 the emission, the more desirable such acathode becomes. As a rule, both the cold and thermionic cathodes havetheir electron emitting surfaces so treated that a low work function isimparted thereto. Such coatings in general comprise a mixture of theoxides of alkaline earth metals or alkali metals or certain of the rareearth metals.

In order to obtain increased electron emission from the cathode, atleast one of two things must be done. If the cathode is to remain thesame, it is necessary to increase the temperature of the thermioniccathode to obtain increased emission. This reacts deleteriously on thelife of the cathode. Another way which is applicable to both the coldand thermionic cathodes is to .reduce the work functioii at thatsurface.

- It is also possible to combine these two methods into a third one inwhich both the Work function is lower and in which the afiinity of thecoating for the cathode surface is such that a higher than'ordinaryoperating temperature Wlll in general be harmless to the coating.

My invention involves this latter procedure. In general'my invention isbased upon the fact that certain. of the noble metals such as palladium,platinum, ruthenium or rho-' dium, have the property of absorbinghydrogen. By providing a cathode surface of any nature whatsoever with acoating of one or more of the above noble metals, I am enabled to obtainan active cathode surface which is more eflicient and more tenaciousthan ordinary coatings. active layer of such noble metal is exposed tohydrogen with a resultant absorption of some of the gas. Thereafter thevapor of an alkali metal is allowed to react on this surface.

As'is well known, alkaline metals form a very efiicient electronemit-tingcathode sur- I face. They labor, however, under the dis-'advantage of being very easily driven off by the heat. By my invention,the alkaline vapm penetrating into the pores of th noble A cathodesurface having an metal is fixed therein, probably in the form of ahydride.

A cathode surface thus formed has been found to be very useful andeflicient, both as a cold or thermionic cathode.

Referring to the drawings, Figure 1 is a sectional view of aphoto-electric cell having my improved cathode.

, Figure 2 is a section of a vacuum tube provided with a similarcathode.

Referring to Figure 1, 1 is a glass tube Within which is disposed acopper member 2. Upon this copper member is deposited or plated,platinum, palladium, ruthenium or rhodium. Of these metals, I preferpalladium since it absorbs hydrogen with the greatest ease. A ring anode3 within the tube is supported by lead wire 4 in a press 5. The tube hasa base 10 having prongs 12 for connection to an ordinary vacuum tubetype socket. Lead wire 4 is connected to one of the prongs. Sealed inpress 5 is a wire 14 supporting a metal capsule 15. Within this capsuleare chemicals which upon suitable heating, evolve caesium, rubidium orany other of the alkali metals. If desired, a mixture of two or more ofthe alkaline metals or with any other metal may be used. The chemicalfor the release of such metals, as a rule, consists of the chloride ofthe alkali metal mixed metallic calcium. Wire 19 supporting cathode 2serves as a lead to one of the prongs in base 10.

The tube is thoroughly exhausted and freed of occluded gases inaccordance with customary practice. Thereafter a quantity of purehydrogen is admitted so that there is a pres- ,sure of about .1 mm. Aglow discharge betemperature is raised so that the chemicals therein.become heated. Chemical interaction results in the evolution of caesiumor oth er alkali metal or mixture of metals which may be used. Thismetal settles upon the surface of the palladium to form an active layerthereon. The. tube may now be seal-e71 and be ready for use if desired.

However, I prefer to admit a small quantity of helium so that the gas isat a pressure of .1 mm. A discharge is then initiated between theelectrodes in the helium. The bombardment of the helium ions formed bythe discharge removes any excess alkali metal from the surface of thepalladium plated copper member 2 and leaves a very thin active layer ofalkali metal. The cell may be exhausted after the discharge has run fora short time and the tube sealedofi'.

Such a tube is sensitive to light variations and makes a very desirablephoto-electric cell in every way. I

Referring to Figure 2, an anode 20 is shown supported on wires 21 and22, the latter being extended through-press 5 to a suitable base foroutside connection. A grid 23 disposed within the anode, is supported bytwo wires 24 and 25 in a similar manner. Within these two electrodes issupported a cathode 28 by wires 29 and 30. This cathode consists of acentral core upon which is supported the layer of noble metal 31. Thiscentral core may be either of -metal, if the cathode is to be directlyenergized, or may consist of the well knownheater type of cathode. Ineither case, the electron emitting surface comprises a layer of one ormore of the noble metals on a suit-able metal base if desired and havingabsorbed a certain quantity of h drogen in combination with one or more0 the alkali metals. The preparation of the cathode for this tube isexactly the same as for the photoelectric cell above. Either one or bothof the tubes may be exhausted to a high vacuum or, if desired, may havea gas at any desired pressure.

I claim: 7

1. In an electron discharge device, a cathode comprising a layer ofmetalhaving hydrogen absorbed therein and a layer of alkali metal thereon.

2. In an electron discharge device, a cathode comprising a layer ofpalladium having hydrogen in solution therein and a layer of alkalimetal formed thereon.

3. In an electron discharge device, a cathode comprising a layer ofpalladium having hydrogen in solution therein and a layer of caesiumthereon.

4. An electron discharge device comprising an anode ,andiQthode, said.cathode com-'' prising a ineltal meiiiber. havin its surface coveredwitlij a layer of palla ium. .,ha'ving hydrogen absorbed therein and aliiyer of caesium formed thereon.

5. The method of making an active cathode surface for an electrondischarge device, which consists in haying a palladium surface as oneelectrode of a discharge in a hydrogen atmosphere whereby hydrogen isabsorbed by said palladium and thereupon condensing a layer of caesiumthereon.

6. The method of making a discharge device, which consists in initiatinga discharge in a hydrogen atmosphere between an anode and a cathode,said cathode having a palladium surface whereby hydrogen is absorbed bysaid palladium, exhausting said device to a high vacuum and thereuponcondensing a film of alkali metal thereon.

7. The method of making an electron discharge device which consists ininitiating a discharge in a hydrogen atmosphere between an anode and acathode, said cathode having a palladium surface whereby hydrogen isabsorbed by said palladium, exhausting said device to a high vacuum andcondensing a film of caesium thereon.

8. The method of making an electron dis charge device which consists ininitiating a discharge in a hydrogen atmosphere between an anode andcathode, said cathode having a palladium surface whereby hydrogen isabsorbed byv said palladium, exhausting said device to a high vacuum,condensing a layer of alkali metal thereon, then introducing a rare gasin said device, initiating an electrical discharge between saidelectrodes in said rare gas and then exhausting to a high vacuum.

9. The method of making an electron discharge device which consists ininitiating a discharge in a hydrogen atmosphere between an anode and acathode, said cathode having a palladium surface whereby hydrogen isabsorbed by said palladium, exhausting said device to a high vacuum,condensing a layer of caesium thereon, introducing a rare gas,

initiating an electrical discharge between said electrodes in said gasand then exhausting to a high vacuum.

10. The method of making an electron discharge device which consists ininitiating a discharge in a hydrogen atmosphere between an anode and acathode, said cathode hav-- ing a palladium surface whereby hydrogen isabsorbed by said palladium, exhausting said device to a high vacuum,condensing a layer of caesium thereon, introducing helium in saiddevice, initiating an electrical discharge between said electrodes insaid helium atmosphere, and then exhausting to a high vacuum.

In testimony whereof, I have signed my name to thisspecification.

- LAURENCE K. MARSHALL.

